8:00 am – 9:30 am
Part I: Moungi Bawendi
Introduction to Colloidal Quantum Dots
This lecture will cover the synthesis, basic photophysics and provide a perspective on the applications of colloidal quantum dots. In particular, we will discuss the synthesis of II-VI (CdSe and the like) and III-V (InAs and the like) nanocrystals and core-shell morphologies based on them. We will focus on the photoluminescence properties of quantum dots from a fundamental perspective, but also in the context of applications that include displays, QDLEDs, and for biolabeling.
9:30 am – 10:00 am BREAK
10:00 am – 11:30 am
Part II: Haibo Zeng
Synthesis and Control of All-Inorganic Perovskite QDs for Flexible High-Definition QLED Displays
Perovskite light-emitting diodes (LEDs) have become a hot field with intensive expectation for flexible high-definition displays. On the one hand, within only one year, electroluminescence (EL) external quantum efficiency (EQE) of hybrid perovskite LEDs has been drastically improved over 10% from the first reported 0.76%. In contrast, all-inorganic CsPbX3 (X = Cl, Br, I) perovskites have higher stability and photoluminescence (PL) quantum yields (QYs), but the EQE and brightness of their LEDs are still pacing at much lower levels since reported first by Zeng’s group. Here, we report the progress on all-inorganic perovskite CsPbX3 QLEDs, including room-temperature synthesis, the improvement of QLEDs via surface control, as well as the great improvement of their stability through Mn doping and control on space distribution. It was found that surface purification can both depress the degradation of PL QYs and improve the injection of charges, which are usually contradictory during the indispensable QDs washing process. Resultantly, after surface purification, the PL QYs are maintained as high as 95% and the current efficiencies reach as high as 13.3 cd/A. Considering the superior merits of high PL QY of over 95%, high color purity with PL FWHM of only 20 nm and high stability, all-inorganic perovskite CsPbX3 QLEDs with high EQE and brightness could be promising for the next generation of flexible and high definition displays.
11:30 am – 1:30 pm BREAK
1:30 pm – 3:00 pm
Part III: Tae-Woo Lee
Efficiency Metal Halide Perovskite Light-Emitting Diodes
Metal halide perovskites are emerging high color-purity emitters with low material cost. However, low electroluminescence (EL) efficiency at room temperature is a challenge that should be overcome. In this presentation, various strategies to achieve efficient perovskite light-emitting diodes (PeLEDs) will be presented. The EL efficiency limitations of PeLEDs using the perovskite emitter in forms of (1) 3D crystal structures, (2) quasi-2D crystal structures and (3) nanoparticles (NPs) can be overcome by controlling the confinement of electron-hole pairs and the charge transport in the devices at the same time. First, to improve EL efficiency of PeLEDs based on 3D crystal structures, a self-organized buffer hole injection layer can be introduced to reduce the hole injection barrier and block the exciton quenching at the interface. The high-efficiency methylammonium lead bromide (MAPbBr3) and CsPbBr3 PeLEDs were realized based on the buffer hole injection layers and the temperature dependence of EL in the CsPbBr3 PeLEDs was systematically investigated and related with ion migration, EL quenching pathways and electron-phonon coupling. Furthermore, the formation of metallic lead atoms causes strong exciton quenching, and it was prevented by finely increasing the molar proportion of MABr in MAPbBr3 solution. Also, the efficiency in PeLEDs can be increased by decreasing MAPbBr3 grain sizes and consequently improving uniformity and coverage of MAPbBr3 layers. Chemically inert graphene avoids quenching of excitons by diffused metal atom species from indium tin oxide. Second, quasi-2D perovskites were studied because of the advantages of quasi-2D perovskites such as the enhancement of film quality, exciton confinement and reduced trap density, and quasi-2D PeLEDs with high efficiency and brightness were demonstrated. Finally, perovskite NPs were effectively used in PeLEDs because they can show high luminescence efficiency and high color-purity in both solution states and film states, and high efficiency PeLEDs based on MAPbBr3 and formamidinium lead bromide (FAPbBr3) NPs were also fabricated.
3:00 pm – 3:30 pm BREAK
3:30 pm – 5:00 pm
Part IV: Tze-Chien Sum
The Photophysics of Halide Perovskite Emitters
This part will outline the fundamental photophysics of metal halide perovskite emitters with a focus on the model CH3NH3PbI3 system. The presentation will not only include polycrystalline, quasi-2D, nanoparticle perovskite systems but also emerging Pb-free systems (e.g., CsSnI3). Challenges and opportunities in achieving optical gain from these excellent light emitters will also be discussed.
- Moungi Bawendi, Massachusetts Institute of Technology
- Haibo Zeng, Nanjing University of Science of Science and Technology
- Tae-Woo Lee, Seoul National University
- Tze-Chien Sum, Nanyang Technological University